Enhancing ground-state interaction strength of neutral atoms via Floquet stroboscopic dynamics

TL;DR

This work addresses the challenge of weak ground-state interactions in neutral atoms by introducing a Floquet stroboscopic protocol that alternates ground-state coupling with a $4\pi$ ground-to-Rydberg pulse. The resulting dynamics confine evolution to the single-excitation manifold and drive the system from the collective ground state $|G\rangle$ to a symmetric ground-state $|W_N\rangle$ state, effectively realizing a ground-state blockade that persists beyond conventional Rydberg blockade radii. The approach demonstrates high fidelity across wide ranges of $U_{rr}/\Omega$ and is robust to experimental imperfections, including decay, phase noise, amplitude noise, and detuning errors, as well as atomic position fluctuations. It also provides a pathway to high-quality single-photon generation and scalable implementation in a Rydberg superatom, highlighting a versatile platform for robust quantum state preparation and photonic quantum technologies.

Abstract

Neutral atom systems are promising platforms for quantum simulation and computation, owing to their long coherence times. However, their intrinsically weak ground-state interactions pose a major limitation to the advancement of scalable quantum simulation and computation. To address this challenge, we propose an approach to enhancing the ground-state interaction strength of neutral atoms via Floquet modulation of a Rydberg atomic ensemble. Each Floquet period consists of ground-state coupling followed by a pulse driving the transition from the ground state to the Rydberg state. Theoretical analysis and numerical simulations demonstrate that after a defined evolution time, neutral atoms within Rydberg ensembles can collectively form a $W$ state in the ground-state manifold. Even when the Rydberg interaction strength is far below the blockade regime, the fidelity remains remarkably high. Finally, we analyze the application of this scheme in the preparation of single-photon sources. In general, our proposed mechanism offers an efficient and highly controllable method for quantum state preparation within the Rydberg atomic ensembles, significantly enhancing the accuracy and stability of quantum state engineering while providing a well-controlled quantum environment for single-photon generation.

Figures (9)

• Figure 1: (a) An ensemble of cold $^{87}\text{Rb}$ atoms is confined in a dipole trap. (b) Schematic diagram of single atomic energy level configuration with ground state $|g\rangle \equiv |5S_{1/2},F=1,m_F=0\rangle$ and $|e\rangle \equiv |5S_{1/2},F=2,m_F=0\rangle$, the Rydberg state is $|nS_{1/2},m_j=1/2\rangle$. (c) The evolution and corresponding pulse sequence of the system under periodic driving.
• Figure 2: (a) Floquet quasienergy spectrum of the system. (b-c) Two representative regions extracted from panel (a), showing the comparison between the Floquet quasienergy spectrum and the effective coupling obtained from the unitary kicks Hamiltonian for different driving periods $N$, in accordance with the quasienergy periodicity relation $\epsilon \equiv \epsilon + 2n\pi/T$. (d) and (e) show population of the states for a two-atom system under $N=20$ and $N=30$ cycles, respectively. We set $\omega/2\pi=1$ MHz, $\Omega= 5 \omega$, and $U_{rr}=45 \Omega$.
• Figure 3: (a) Fidelity of the state $|W_2\rangle$ versus $U_{rr}/\Omega$ and cycle number $N$, showing high overall robustness ($F>99\%$) but revealing several sharp, $N$-independent resonant leakage channels, as shown in the broad scan (i) and detailed view (ii). (b) Quasienergy spectrum as a function of $U_{rr}/\Omega$, revealing a distinct avoided crossing. (c-d) Detailed views of the quasienergy spectrum as a function of $U_{\mathrm{rr}}/\Omega$. Other parameters are the same with Fig. \ref{['fig2']}.
• Figure 4: (a) The fidelity of the state $|W_\mathbb{N}\rangle$ during evolution with and without decay from Rydberg state $|r\rangle$. We set the decay rate $\gamma/2\pi=1$ kHz for the room-temperature (300 K) case. Fidelity of the target state $|W_\mathbb{N}\rangle$ during the evolution for $\mathbb{N}=4$ atoms under different noise conditions: (b) Rabi amplitude noise, (c) laser phase error, and (d) laser detuning error. Other parameters are the same with Fig. \ref{['fig2']}.
• Figure 5: (a) An ensemble of cold $^{87}\text{Rb}$ atoms is confined in a dipole trap. The generated single photons are detected by detectors D1 and D2. (b) The evolution and corresponding pulse sequence of the system under periodic driving. (c) Level diagram. (i) Atoms are initially in the ground state $|g\rangle$ and prepared in the singly excited state $|e\rangle$ via optical pumping. (ii) The ground-state excitation is retrieved through the application of the read field $\Omega_c$, and subsequently measured at detectors D1 and D2. (d) The second-order correlation function of the radiated light. Other parameters are the same with Fig. \ref{['fig2']}.